Sea Ray 270 Sundancer 1988 propeller question.

[tottes]

1988 270 Sundancer with Twin 4.3l 175 hp alpha one. I'm about to change props. From 3 blade (according to photo 20x19, can not be correct?) to 4 blade. What prop size is recommended?
Thinking about to replace with solas 4-blade 14.25x19..

I hope to mainly reduce fuel consumption.

 

[Lazy Daze]

The "20" is just part of the part number, it does not indicate diameter. Probably about a 14" diameter. "Typically", you drop an inch or two when going to a 4-blade. But this is not a hard and fast rule - too many variables to deal with. First thing you need to do is get some data. Run the boat WOT, trimmed as high as you can - you want MAX RPM and MAX MPH. Run the boat with your normal load for this test. Once you have those numbers, re-post. The more accurate you can be with this, the better off you'll be. You MUST get these numbers, especially since it's an older boat/engines and all engines can lose power over time. Also, get some cruiser numbers speed/rpm at varying speeds - especially at the current cruise RPM you like for best fuel consumption.

 

[tottes]

wot 4800rpm 32knots
i cruise at 3600rpm 24-26 knots . fuel consumption is about 2,5l nm (Excuse the European data)

 

[Winch1995]

You should be able to find the original prop specs online. Be careful because most times if you use a new prop you can’t return it. I went with SS and I am happy.

 

[Lazy Daze]

Your numbers sound really good. The newer V6's have a recommended max rpm of 4800. It's possible the older ones had a slightly lower recommendation. But this is not a problem - either way it's a good thing because you have a little rpm to play with. Whatever you end up with, you don't want to have a max rpm too low.

Can you get a 4-blade in odd number pitches? It used to be that they only came in even numbers. However, given you have some RPM to play with, I would be very curious to try (if available) the 19" or even possibly a 20". You might end up at 18", but prop selection is never a black and white thing - it often takes some experimentation due to all the variables. If you don't have a shop nearby where you can experiment, I would contact a retailer that specializes in this area such as Prop Gods.